(1) Field of the Invention
The instant invention relates to variable speed drives. More particularly, the instant invention relates to variable speed drives utilizing conical rolling surfaces.
(2) Technical Considerations and Prior Art
Applicant's prior applications, U.S. patent application Ser. Nos. 426,875 and 480,144 now U.S. Pat. No. 4,459,840 respectively disclose the concept of utilizing a non-slipping, conical transmission member in a single-speed drive and a multi-speed drive, respectively. The drives disclosed in these patent applications have numerous advantages over conventional gear drives and other types of transmissions such as conventional traction drives and drives which rely on belts and cones. However, for certain applications, such as automatic transmissions used with piston driven engines, there is a pressing need for variable speed transmissions in which the output speed of the transmission can be varied continuously with respect to the input speed, rather than being varied in a step-wise manner, such as is disclosed in U.S. patent application Ser. No. 480,144 now U.S. Pat. No. 4,515,028.
Perhaps the closest family of prior art devices are traction drives which have been discussed in detail in the book Traction Drives, Selection and Application, by F. W. Leilich III and E. E. Shube; Marcel Dekker, Incorporated; 1983. All of the traction drives disclosed in this book utilize a "traction fluid" to transmit forces from input members to output members. The traction fluid is necessary because the members slip relative to one another and must therefore be lubricated with a fluid to minimize heat and to minimize wear of opposed surfaces. Since the lubricating fluid must also transmit tangential drive forces between the members, the fluid must have a very high viscosity pressure index. Appropriate lubricating fluids have only recently become available, however, these lubricants, like any lubricants, are subject to degredation and failure. Moreover, these traction drives must provide auxillary structure and devices for handling lubricating fluids resulting in additional design complications, increased weight, reliability problems, maintance concerns, and expense. In addition, since these traction devices "slip", they have an inherent inefficiency which is undesirable in and of itself, and which generates heat that must in some manner be compensated for or disposed of.
Another approach, which of late appears to show commercial promise as a variable speed drive, is a belt driven arrangement wherein a wear-resistant, fabric or metal belt is nested between pairs of pulleys having conical surfaces which are capable of moving toward and away from one another. This movement varies the diameter at the driven or driving pulley pairs and thus changes the speed of a driven shaft with respect to a driving shaft. While no lubrication is used between the opposed surfaces of the belt and pulleys (negating the aforementioned difficulties caused by lubrication), belt drives have other problems. Since the belts necessarily slide on the pulley surfaces as speed is varied in these drives, there is wear which eventually degrades the belts necessitating their replacement. Moreover, the belts are continually worked as they flex in their passage around the pulleys. This consumes power and generates heat, which heat further degrades the belt. The slippage, flexing and heat introduce inefficiencies in belt drives, thus reducing their desirability.
In view of the aforementioned drawbacks of prior art devices, there is a pressing need for improvement in such devices.